Frequency planning for radios may refer to the selection and use of various signal frequencies including, for example, the output frequency of a Voltage Controlled Oscillator (VCO), the frequency and/or generation scheme of local oscillator (LO) signals, the values of one or more intermediate frequencies (IF) in the radio's signal paths, and so on. Direct-sampling receivers sample a received signal without down-converting the received signal. In contrast, direct-conversion receivers use LO signals to down-convert the received signal (e.g., from radio-frequency (RF) to baseband frequency) to generate in-phase (I) and quadrature (Q) signals, and then sample the I and Q signals at the baseband frequency. Down-converting the received signal allows for a lower-frequency sampling clock (as compared to direct-sampling receivers), but introduces signal impairments resulting from local oscillator noise and/or I/O mismatch.
The VCO may be used to generate the LO signals for down-conversion in the receiver and for up-conversion in an associated transmitter. When the VCO frequency is equal to or is an integer multiple of the RF frequency, direct-conversion transceivers may be prone to VCO pulling. Thus, it would be desirable to generate LO signals in a manner that minimizes VCO pulling. In addition, it may also be desirable to generate multiple phases of the LO signals in a manner that minimizes VCO pulling.